A variety of computer and video systems exist today, which employ input devices, such as props. The props are held and manipulated by the user, and carry a color or pattern which is easily tracked by a color recognition system, and whose motion is easily followed by the color recognition system. The motion of the prop is translated into control inputs for a video or computer device. For example, in a video game or virtual reality system, a prop can be wielded by the user, and the motions of the prop can be used to direct motions of a character displayed on a screen. In contrast to wired props, which are expensive and which limit the user's movement, passive props can allow the user to move anywhere within the field of view of a camera which is part of the video system. Also, in contrast to wired, radio frequency ("RF") or infrared ("IR") control devices, which are relatively expensive, and which contain a certain amount of electronic circuitry, passive props can be inexpensive to produce, simply being made of plastic or paper with a design printed on the prop. Also, in contrast to the traditional wired joystick, which is a nuisance to attach and remove from the video system or computer, the passive prop is freely interchangeable. The user need merely cast one prop aside and take up another in order to make the change. Also, because of the simplicity and ease of manufacture of the prop, props can be manufactured and offered very inexpensively, enabling the user to afford a whole collection of props.
Various difficulties exist in the present use of passive props. For example, not every prop offers all desirable degrees of freedom. It may be desirable, for example, to allow a prop to be used to control a cursor on a television screen. In such a prop, five degrees of freedom would be desirable. Movement of the prop in the x, y and z directions can control gross movements of the cursor, and adjusting the pitch and yaw of the prop can be used to control fine movements of the cursor.
One difficulty with the use of passive props is the difficulty with disambiguation that occurs in some prop designs. Tracking of a passive prop may be performed through conic solutions. The design of many props results in two similar or identical conic solutions. It is difficult to disambiguate these solutions to accurately track the motion of the prop. A further difficulty is that presently existing props do not provide a sufficient range of control options. Thus, there exists a need in the art for improved passive prop designs which suffer from minimal ambiguity, which provide a convenient and precise method for controlling a cursor, and which provide an increased range of control.